Stormwater Filtration Systems

ABSTRACT

A stormwater filtration system suitable for treatment of stormwater runoff in a developed environment uses a primary treatment bay that includes a filtration bed with live plant matter. A second treatment bay treats water that exceeds the maximum throughput of the primary bay. A reservoir stores treated runoff to water the plants during dry weather. Removable trays on the surface of the primary filtration bed provide plants suitable for ground cover. Additional bays expand the filtration bed throughput and accommodate extended root systems. A flow control may be provided for the primary treatment bay.

CROSS-REFERENCES

This application claims the benefit of U.S. Provisional Application Ser.Nos. 61/043,612, filed Apr. 9, 2008, 61/056,236 filed May 27, 2008 and61/140,276 filed Dec. 23, 2008, each of which is incorporated herein byreference.

TECHNICAL FIELD

This application relates generally to stormwater filtration systems and,more particularly, to systems incorporating live plant material into thefiltration process.

BACKGROUND

Stormwater can be a form of diffuse or non-point source pollution. Itcan entrain pollutants, such as garbage, sediment, organic matter, heavymetals, and organic toxins, and flush them into receiving water bodies.As a consequence, natural bodies of water that receive stormwater mayalso receive pollutants.

In an effort to address the environmental problems posed by pollutedformat traps and filters for stormwater have been developed.

Stormwater filtration cartridges, such as those described in U.S. Pat.Nos. 5,707,527, 6,027,639, 6,649,048, and 7,214,311, pull stormwaterthrough a filtration bed that removes pollutants prior to discharge intoa receiving water body. Improvements to such cartridges have producedhighly effective filters that allow for significant throughput, asdescribed in the references cited above, while also allowing for easyinstallation and replacement of the modular cartridge units,

Another known method of stormwater filtration involves the installationof horizontally-disposed filtration beds using a mixture of materialsoften including organic compost. Stormwater runoff directed into thesebeds is filtered in an action not unlike natural soil. Live plantmaterial is sometimes added to take advantage of its pollutant uptake aswell as for aesthetic value, While mixtures for these filtration bedscan be developed that accommodate a higher throughput of stormwater thannatural soil, the level of throughput is still limited by the area ofthe bed and nature of the filtration bed material. Additionally, inareas where rainfall is sporadic, the stormwater received may not besufficient to maintain the live plant matter therein.

It would be desirable to develop a contained, aesthetic stormwatertreatment system using a filtration bed including live plants thatnonetheless allows for higher throughput when necessary and adequatefiltration of that higher throughput to the extent practical.

It would also be desirable to develop a stormwater treatment system thatcan maintain the live plants therein during periods of low rainfallwithout excessive irrigation needs.

Additional desired improvements to stormwater treatment systems withlive plant matter include methods to easily place and later remove plantmatter suitable for ground cover, and supplemental beds that expand thearea of treatment and can accommodate the extended root systems of thelive plants found in the filtration bed.

SUMMARY

A stormwater filtration system is provided that includes a first orprimary treatment bay with live plant matter in a filtration bed, and asecond overflow or secondary treatment bay that receives and treatsstormwater that exceeds the capacity of the first treatment bay.

In a further aspect, the first or primary treatment bay and overflow orsecondary treatment bay are enclosed in a common vault structure, whichincludes an inlet for stormwater to enter the vault and first treatmentbay, means for untreated overflow stormwater to enter the overflowtreatment bay from the first treatment bay, and an outlet for treatedwater to leave the vault.

In another aspect, a outlet bay is provided in combination with thefirst treatment bay and second treatment bay, and water entering thesystem is directed into an inlet compartment in an upper portion of theoutlet bay before entering the first treatment bay or secondarytreatment bay.

In another aspect, a removable root tray containing small plantssuitable for ground cover is provided which interfaces favorably with afiltration bed including live plant matter.

In yet a further aspect, a stormwater filtration system is provided thatincludes both a first vault including a filtration bed with live plantmatter and also secondary vaults, which vaults may be configured toaccommodate the extended root structure of the plants of the firstvault.

An optional feature would be to incorporate a wetwell that collectstreated water that can later be wicked to root zone(s) during dryperiods.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below, Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows one embodiment of a treatment system from above.

FIG. 2A is a side elevation view of the system of FIG. 1A.

FIG. 1B shows another embodiment of a treatment system from above.

FIG. 2B is a side elevation view of the system of FIG. 1B.

FIG. 3 is a side elevation view of the a treatment bay including areservoir,

FIG. 4A shows a configured root tray system from above.

FIG. 4B is a side elevation view of a treatment bay including a roottray system.

FIG. 4C is a top-down view of a root tray.

FIG. 4D is a side elevation view of a root tray system includingreservoirs.

FIG. 5A is a top-down view of a filtration system including secondaryvaults or bays with porous pavers.

FIG. 5B is a side elevation view of the filtration system of FIG. 5A.

FIG. 5C is a side elevation view orthogonal to FIG. 5B along line A-A.

FIGS. 6A and 6B are views of an embodiment including a top pan.

FIGS. 7A-7B illustrate a further embodiment of a treatment system,

FIG. 8 is a schematic depiction of an embodiment of a treatment systemincluding separate inputs for the primary, secondary and outlet bays;and

FIG. 9 is a schematic depiction of a treatment system using distinctvault structures.

DETAILED DESCRIPTION

In one aspect shown in FIGS. 1A and 2A, a filtration system 10 isprovided in a concrete vault 12 that has an internal vertical wall 14dividing the vault into a primary treatment bay 16 and an overflow orsecondary treatment bay 18. A top wall 20 of the unit is also formed ofconcrete. Other materials could be used to form the vault, and the twobays could be formed as separate structures or vaults placedside-by-side and connected by corresponding adjacent wall openingsand/or piping.

The primary treatment bay side of the top wall includes an opening 22and associated tree ring 24 through which the trunk or stem of a tree orherbaceous plant extends. A manhole or hatch 26 above the overflowtreatment bay gives access to the filtration means located therein.Dimensions for the vault could vary as needed. The overflow treatmentbay 18 shown utilizes a suitable stormwater filter cartridge 42, such asthe StormFilter product available from. Contech Stormwater Solutions,Inc. of West Chester, Ohio, and described in U.S. Pat. No. 7,214,311.Other possible cartridges that could be used include the Perk Filteravailable from Kristar Enterprises Inc. of Santa Rosa, Calif. or the CDSor MFS filtration cartridges also available from Contech StormwaterSolutions, Inc. It is also recognized that the overflow treatment bay 18could utilize other forms of stormwater filtration devices, includingnon-cartridge type devices. Upflow type filters could also be used. Incertain embodiments, the filtration means of the overflow treatment bayis readily replaceable, as is the case with the cartridge-type filters.

Preferably, the treatment capacity of the overflow bay is substantiallygreater than the treatment capacity of the filtration bed bay. Forexample, the treatment capacity of bay 18 may be at least two timesgreater than the treatment capacity of bay 16, and more preferably atleast two and a half time greater (e.g., three, four or six timesgreater). In order to accomplish such a result, it is beneficial for theoverflow treatment bay to utilize a different type of filtration device(e.g., self-contained filtration units in the form of cartridges) thanthe filtration bed of bay 16. In one example, the filtration bed bay maybe configured to have a treatment flow capacity of between about 12 and20 gallons per minute, and the overflow treatment bay may be configuredto have a treatment flow capacity of between about 40 and 50 gallons perminute.

As shown, the filtration system 10 is of a size and structure suitablefor placement in an urban environment, such as along a street or parkingarea to receive surface runoff or next to a building to receive the roofrunoff. The vault prevents accumulated stormwater from destructivelyinterfering with adjacent urban systems, and the generallyself-contained configuration allows for easy placement as part ofexisting stormwater drainage solutions. The filtration system may bemodified in configuration, structure, or size to accommodate thespecific stormwater treatment needs of a target area without deviatingfrom the invention as described and claimed herein.

Referring again to FIGS. 1A and 2A, water flows into the primarytreatment bay via a curb inlet opening 29 and onto a band of rip-rap 28to reduce water speed and erosion. In one embodiment, the tree isplanted within a multi-layer bed 30 in the treatment bay. A top layer 32of the bed may be 12 to 24 inches of a 60% (by volume) CSF leaf media orvariant—40% (by volume) sand mix, The CSF leaf media component is madeexclusively of composted, fallen deciduous leaves in granulated form,and is available from Contech Stormwater Solutions, Inc., of WestChester, Ohio, A next layer 34 of the bed may be 6 to 18 inches of sand.A bottom layer 36 may be 6 to 10 inches, or more, of gravel, whichcontains and covers a perforated pipe or pipe system 38 that collectswater that has filtered through the bed.

In another embodiment only two layers are provided. For example, anupper layer formed by a media mixture consisting essentially of 18-33%(e.g., 25%) by volume of pelletized leaf compost (e.g., CSF), 50-65%(e.g., 57%) by volume pelletized pumice, 10-25% (e.g., 18%) by volumesand and less than 1% by volume water absorbent crystal material. Theupper layer may be, for example, 25 to 35 inches deep (e.g., 28″ deep).The upper layer may sit upon a lower gravel layer that is, for example,4 to 8 inches deep (e.g., 6″ deep).

Other variations in the make-up of the bed 30 are possible andcontemplated, including beds with more or fewer layers, beds of uniformcomposition throughout their depth, and beds that utilize othermaterials.

The pipe system 38 includes an outlet segment 39 that runs through thedividing wall 14 into the secondary treatment bay 18 and joins with theoutlet conduit 40, at a downstream side of the cartridges 42, forsubsequent flow to the outlet of the vault. An outlet control valve 41is positioned to control flow through the primary treatment bay to adesired flow rate according to applicable regulatory requirements. Anoutlet control orifice could be used in place of the valve 41, with theorifice sized to limit flow. Where a valve is used, the valve could bemade as a one way valve that prevents reverse flow from the secondarytreatment bay to the primary treatment bay. The valve or orifice 41 islocated on the secondary treatment bay side but could readily be locatedon the primary treatment bay side. The pipe system 38 also includes oneor more cleanouts 43 that extend upward above the top of the bed foraccessibility. The cleanout access could alternatively be located on thesecondary treatment bay side of the system. The valve or orifice featurecould also be incorporated into systems that include only a primarytreatment bay, without any secondary treatment bay.

The dividing wall 14 is formed to include an secondary path 44 to thesecondary treatment bay. The secondary path may be a pathway at or nearthe top of the wall. The pathway may include an inclined screen 46(e.g., made of stainless steel with aperture size of about 5 mm).Excessive flows into the primary treatment bay (i.e., flows that exceedthe treatment capacity of the primary treatment bay) will result in anoverflow into the secondary bay 18, where the overflow stormwater movesthrough one or more filter cartridges 42 for treatment. The watertreated by the cartridges 42 meets the water treated by the primarytreatment bay 16 downstream from both treatment means for mutualoutflow. A bypass weir 48 is located in the secondary treatment bay 18such that flows into the secondary treatment bay 18 in excess of theflow capacity of the filter cartridges 42 will pass directly to anoutlet bay 49 and then to the vault outlet 51. In the illustratedembodiment the outlet conduit 40 delivers the treated water to theoutlet bay 49.

FIGS. 1B and 2B depict an alternate embodiment of a stormwaterfiltration system in which the outlet segment 39′ of the perforate pipesystem extends through wall 14 and delivers water directly into theoutlet bay 49 for subsequent flow through outlet 51. A flow controlorifice 41′ is sized to act as a limit on flow rate through the bed ofthe primary chamber 16 (e.g., to a level below the initial infiltrationcapacity of the bed). The outlet conduit 40 passes through the weir wall48 to deliver filtered water from the cartridges into the outlet bay 49for subsequent flow through outlet 51.

Referring now to FIG. 3, in connection with a stormwater filtrationsystem that utilizes live plant material such as a tree, an advantageousfeature may be provided in the form of a lower water reservoir 50 (e.g.,below the outlet of the treatment bay) that is, in certain embodiments,either within a layer of open rock material or separated from the bay bya frame and fabric. Other structures for forming the reservoir could beprovided. The bay outlet 52 is located above the reservoir 50 to assurethat the reservoir is not drained as a result of the outlet path 52.Instead, stormwater that enters the unit filters through the bed 54 andsome amount will collect in the reservoir 50. In one implementation, aventing pipe (not shown) may extend upward from the reservoir 50 inorder to reduce the likelihood of anaerobic conditions occurring in thereservoir if the filtration bed becomes occluded.

During drier conditions, the bed 54 containing the live plant materialmay not receive sufficient water to maintain the live plant material.However, the reservoir can be used to maintain the plant material byproviding a wick-type structure 56 with a lower end 58 positioned in thereservoir to absorb water and an upper end 60 positioned in proximity tothe root material. In one embodiment, the wick-type structure could beas simple as a rope material with upper and lower ends being frayed.Capillary action of the wick-type structure draws water from thereservoir into the bed as the bed dries out. Alternatively, an activetransport system such as a fluid pump or other irrigation feature may beused in place of the wick-type structure. In some cases, theconfiguration of the soil and live plant material may allow access tothe water without the need for any additional structure. For arid andsemi-arid regions, native plants or dry tolerant plants should beconsidered.

This reservoir feature could be combined with the two bay system ofFIGS. 1 and 2 or any other embodiment described herein, in which casethe perforated pipe system 38 should be located above the reservoir 50.The size and depth of the reservoir 50 could be configured to match withthe anticipated duration of dry periods of the installation locationand/or the water needs of the particular live plant material that isused.

It is recognized that instead of, or in addition to the tree, other liveplant material could be used, including grasses and shrubs. The opening22 and associated tree ring 24 may be replaced by another opening andconfiguration suitable for the live plant material used. Another optionwould be to provide the primary treatment bay without any live plantmaterial. For example, a rock surface could overlay the filter bed,particularly where irrigation is unavailable or undesirable. This plantfree embodiment could still utilize a water reservoir and wickingapparatus to reduce runoff volumes and encourage biotic activity in thesoil.

Referring now to FIGS. 4A-4D, an additional feature that can be providedin such stormwater filtration systems is a root tray structure.Specifically, a tray or trays 80, which may be formed of plastic, may beprovided for holding plant material at a top portion of a treatment bay.The trays may be formed and located to provide a passage 82 for a treetrunk as shown. Alternatively, other passages may be built into the traystructures to accommodate larger plants such as trees or shrubs that areused in the filtration bed. The trays may be formed with an internalgrid structure 84 to provide structural integrity. The bottoms of thetray include openings to allow water to pass downward to the main bed 86and to allow root growth into the main bed 86. The trays may also beprovided with lower water reservoirs 88 for dry conditions.

The root tray structure is filled with earthen material and may includeplants with shallow roots or fibrous roots systems, such as grass orother ground cover. The trays 80 may be designed to accommodate smallerplants known to perform a particular function, such as filtration ofspecific contaminants, or to provide an additional aesthetic benefit,such as smaller flowering plants, The tray system is easily replaceablein the event that replacing the plant matter therein is desired, such asthe failure of the plant material growing therein, oraesthetically-motivated seasonal alteration of the surface of thetreatment bay.

Use of the root tray structure and associated plant matter for groundcover may motivate the use of a more open structure for a treatment baythan that illustrated in FIGS. 1-2. For example. as shown in FIG. 4B,the upper wall of the vault may be primarily or entirely absent to placethe plants in open communication with the outside environment. Thesystem can be configured to receive runoff through the top opening fromsheet flow or at pointed locations after flow energy reduction viariprap.

Referring to FIGS. 6A and 6B, a top pan concept is shown. Specifically,at the top of the filter bed a pan structure 100 could be used forerosion control. The pan structure 100 includes a base 102, upturnedsidewalls 104 and plurality of openings 106 to permit water flow to thefiltration bed. The pan structure may receive water directly from thecurb inlet via a break or gap 108 in the upturned sidewall 104, or thepan structure may be placed alongside the rip rap. While shown as asingle piece with the tree trunk extending upward through an opening 110therein, the opening having an upturned sidewall 112, it is recognizedthat the pan structure could be formed of two or more pieces that meatat the tree trunk opening, so that the pan structure could be morereadily removable. The tray may installed atop the filter bed, aroundthe tree trunk and below the metal grates 114 that provides the openingfor the tree. Where the pan footprint is substantially the same as thatof the metal grate 114, removal of the pan may be more readily achievedby removal of the grate, and access to the pan for cleaning is alsofacilitated. However, variations are possible. How much surface area ofthe bed is covered by the pan may depend on how large the grates are.Large rectangular grates could allow the entire bed to be covered (ifdesired). The pan could also be manufactured with different tree/plantopenings. For example, one centered opening for a tree is shown,patterns of multiple openings for smaller plants could be provided.

In another aspect, a stormwater filtration system including live plantmaterial may involve multiple vault chambers, or a larger vault withmultiple bays, designed to extend over a larger area or footprint. Insome implementations these additional vault chambers or bays may beconfigured to accommodate extended root structures. As shown in FIGS.5A-C, primary vault chamber or bay 70 includes a tree 71 implanted inthe filter bed therein. The tree is accommodated by a tree ring 73 andgrate structure that cover the bay. Adjacent to the primary treatmentbay 70 are multiple secondary vault chambers or bays 72 designed toaccommodate the extended root system of the tree and provide additionalfiltration over a wider area.

The secondary vault chambers or bays 72 may be covered by a porouspavement material 74 which allows stormwater to enter, In oneembodiment, interlocking concrete pavers can be used. The porouspavement material can be formed into a sidewalk or other surfaceappropriate for human use in an urban environment. The secondary vaultchambers or bays 72 may initially contain little or no root structurewhen a young tree is installed, but may be built to accommodate thetree's root structure as it matures (e.g., the vault wall or wallsseparating the bay 70 from respective bays 72 may include openingstherethrough to allow passage of the roots). To better accommodate rootgrowth, the secondary vault chambers 72 may include a gap between theporous pavers and the surface of the soil, so that root expansion isunlikely to damage or displace the pavers. The pavers can be supportedon inner ledges 90 formed by the walls 92 of the vault so as to providerequired structural reliability while maintaining the gap. The porouspavers may be removable for easy maintenance or replacement of theporous pavement material, or to allow for removal or replacement of thefiltration bed or the tree therein.

Depending on the nature of the filtration system, the walls separatingthe primary and secondary vault chambers may include openings toaccommodate the root system, or may be partially or entirely absent. Thevault chambers may be part of a tandem structure or may be distinct andmodular in construction. In one embodiment, the same shape and materialis used for each vault chamber, both primary and secondary, withdiffering top wall coverings to accommodate the differing live plantmatter in the filtration beds. In another embodiment, the primary vaultchamber may be structurally distinct from the secondary vault chamber.

Any of the structures disclosed above may be included in the primary andsecondary vault chambers shown here, including the inlet and outflowmeans, the secondary treatment bay, the reservoir and wick system, andthe root tray system. The filtration beds may be of similar compositionor may differ between the primary and secondary vault chambers. Avariety of perforated pipe configurations may connect the chambers.

Referring to FIGS. 7A-7B, another embodiment is shown in whichstormwater enters the vault unit through an inlet opening 100 into aninlet tray or compartment 102 above the outlet in the outlet bay 104.The water leaves the tray and flows laterally into the primary treatmentbay 106 via opening 108 in wall 110. Water traveling downward throughthe primary treatment bay bed enters a pipe system 112 and is directedinto the outlet bay 104 though primary bay outlet 114. Once in theoutlet bay water can exit the unit via outlet opening 116, Water thatenters the primary treatment bay in excess of its treatment capacityrises and spills into the secondary treatment bay 117 via overflowopening 118 to pass to the filter cartridges 119. The secondarytreatment bay is sealed from the outlet bay by a metal (or other) wall120, except that water passing through the filters enters a pipe 122 andthen flows to the secondary bay outlet 124, which flows into the outletbay 104. If the water inflow to the unit exceeds the combined capacityof both the primary treatment bay and the secondary treatment bay, thewater will rise higher in the primary treatment and cause the waterlevel in the inlet tray 102 to rise, The inlet tray 102 is configuredwith an overflow path 126 directly into the lower portion of the outletbay 104, and water can flow over a top of the tray directly into theoutlet bay for exiting the unit without passing through either theprimary treatment bay or the secondary treatment bay. The lower edge ofthe overflow path 126 is above the lower edge of the overflow opening118 in the wall 110.

In one example, the inlet tray or compartment 102 may be formed as ametal tray structure mounted to the wall of the vault. The floorcomponent 130 may be removable such that, during installation, and priorto completion of the unit, the floor component may be left out of theunit such that stormwater entering the inlet compartment proceedsdirectly down to the outlet 116 of the outlet bay 104 without enteringthe primary treatment bay 106. Once the unit is ready it can be broughtonline by installing the floor structure.

In an alternative arrangement, the unit shown in FIGS. 7A and 7B couldbe modified such that the overflow opening 118 in the wall 110 iseliminated (i.e., no direct overflow path from bay 106 to bay 117) andan overflow path 132 directly from the inlet compartment 102 to the bay117 is provided. In such an arrangement, the incoming water in excess ofthe primary treatment bay flow capacity would not enter the primarytreatment bay in order to travel to the secondary treatment bay.

Referring to the schematic of FIG. 8, in another alternative embodimenta system 140 includes a primary treatment bay 142 with an associatedfiltration bed and live plant material, a secondary treatment bay 144with filter cartridges 146 and an outlet bay 148. A first vault inlet150 leads directly into the primary bay 142, a second vault inlet 152leads into the secondary bay 144 and a third vault inlet 154 leadsdirectly into the outlet bay 148. The outlet piping system 156 of theprimary bay 142 connects to the piping 158 that receives filteredstormwater from the cartridges 146 and flows into the outlet bay 148.This arrangement eliminates the overflow paths within the vault, andinstead uses a flow control defined by the three openings so that flowin flow direction 160 excess of the primary bay capacity will movedownstream to second inlet 152. and flow in excess of the combinedcapacity of the primary bay 142 and secondary bay 144 will movedownstream to third inlet 154,

The schematic of FIG. 9 is illustrative of a system in which the primarytreatment bay 170 and secondary treatment bay 172 are formed by separatevault structures that are interconnected by piping 174 for overflow tothe secondary bay 172 and piping 176 for delivering bed filtered waterto an outlet bay 178.

It is to be clearly understood that the above description is intended byway of illustration and example only and is not intended to be taken byway of limitation, For example, another advantageous feature would be tostratify the plant root zones to accommodate a deeper and more complexroot zone to promote infiltration, nutrient uptake and planttranspiration. In addition, use of different plant species to create theroot zone stratification can also be used to manage the filter bedsurface to reduce clogging with complex stern structures which bymechanisms of shrinking, swelling, mechanical movement by wind, newgrowth and senescence promotes continuously open pores and openings inthe soil surface. Moreover, while the primary embodiment shown anddescribed above include a vault structure in which the primary treatmentbay includes a solid bottom wall, it is recognized that the solid bottomwall could be made porous, or with one or more openings, or eveneliminated in applications where it would be desirable to have sometreated water infiltrate into the ground below the device. The outletbay could similarly be formed to allow such infiltration. Othervariations are possible.

What is claimed is: 1-42. (canceled)
 43. A method of treatingstormwater, comprising: providing a vault including a filtration bedtherein, a top of the filtration bed exposed to air via an upper openingof the chamber, the filtration bed including live plant matter plantedtherein, the filtration bed including an initial infiltration capacity;initially receiving stormwater to be treated at a location adjacent thefiltration bed; subsequently flowing the stormwater through thefiltration bed into a pipe system within the filtration bed; andlimiting flow through the filtration bed to a level that is less than aninitial infiltration capacity of the filtration bed.
 44. The method ofclaim 43 wherein the pipe system defines a flow construction to performthe limiting step.
 45. The method of claim 43 including: flowing atleast some stormwater through a porous pavement material.